What makes the 325 amp Dual Rectifier alternator different from the 200 or 250 amp dual rectifier alternators?

Most of the components are the same between all the amperage dual rectifier alternators, the big difference is in the stator and bridge rectifier. The stator is the component that the power comes from and the bridge rectifier is the component that converts the AC current that comes out of the stator into DC current. The 325 amp alternator has a much larger Stator core and copper windings. Plus it uses a special winding method where each of the three phases that are in a stator are made up of 4 wires each then connected together in parallel to make one coil set for each phase.
"Quad winding" each phase, as it is called, makes the alternator produce more power at lower rpm's plus with each phase made up of 4 wires instead of one wire helps to dissipate heat much better. The "quad wound" stator produces current much like stranded wire passes current better than solid wire.